A 25 yard zero will not exactly zero your rifle at 100 yards. A 25 yard zero will only put you on paper at 100 yards. The best way to zero the m-16 type rifle is as follows. using the M-4 with issue military iron sights. Place your rifles elevation knob Down to 8/3. Center you windage knob and place the small peep sight in the up position. Notice there is not a 1/4 inch gap between the rear sight and your receiver, if there is then your elevation is on 800 yards. Once on 8/3 go DOWN two clicks by following the DN arrow this will put you on a 100 yard setting. From here ALL changes in elevation will be made with the front sight post NOT the rear elevation knob on your rifle. With the help of your spotter fire at least three well aimed shots at your known 100 yard target. Determine if you are hitting low or high of your target. MAKE YOUR WEAPON SAFE BEFORE GOING FURTHER. On the front sight post of your rifle you will see an arrow with the word UP. If you need to raise the strike of the round up then using a small Phillips screwdriver or some other appropriate tool, press down on the detent pin and move the front sight post in the direction of up. If you need to move the strike of the bullet down go in the opposite direction of up. Be bold in moving the front sight because the adjustments are small and be careful not to scratch your rifle. Fire three more rounds at your known 100 yard target. If you need to make any more adjustments in the elevation of the bullet strikes make your weapon safe and do so with the front sight post only. All adjustments in windage should be made with the windage knob. To move the strike of the bullet right go in the direction of the arrow and the word right, to move the strike of the bullet left move the windage knob in the opposite direction. This will give you an exact zero at 100 yards.

jeremy2171

If you have an A2 rear sight it should go down to "8/3" then minus 3 more clicks.

If it's an A4 then it will be "6/3" -6 clicks.

If your rear sight bottoms out at 8/3 and moves no more then your rear sight is improperly calibrated.

The Army uses this method but the Marine Corps adjusts them so they will go down to the -3 or -6.

To calibrate it:
Set sight to 8/3 (or 6/3) then flip the small aperature up so you can look down at the top of the sight and you will a small set screw. Get a 1/16" hex key and loosen the setscrew a few turns.

Then take the elevation drum and turn the BOTTOM (it has an upper and lower part) to the rear about 1/8 turn then snug up the setcrew. See how many clicks down you now have. Adjust the drum again if you need too.

candyman

Well I did some digging into some of my old military crap and found the 15 yard BZO target for the M16 and the 25 meter zeroing target for the M16A2.

Here are some pic’s

I remember that on the A1 target we fired three rounds. Impact should be on the dotted line and group size should be no bigger then a dime.